21 [s points
Use the following counter to design a counter to count-down from 5 to 2 using D Flip
Flops
(3) 3-Bit Count up (3 to 5) Using D Flip-Flop:
The State Equation of D Flip-Flop:
Q(t+1)=D(t) => Dn=Qn
Present State Next State D Flip-Flop
n Q2p Q1p Q0p Q2n Q1n Q0n D2 D1 D0
3 0 0 0 0 1 1 0 0 1
4 0 1 1 1 0 0 1 0 0
5 1 0 0 1 0 1 0 1 1
D2=Sum(3,4) and don't care X=Sum(0,1,2,6,7)
D1=Sum(5) and don't care X=Sum(0,1,2,6,7)
D0=Sum(4,5) and don't care X=Sum(0,1,2,6,7)
Using K-map to simplify the functions:
D2=Q1+Q0
D1=Q1'Q0
D0=Q1'
Q1
Q1
Q1
Q0
Q0
Q0
D2 Q2
CK Q2
BCD
D1 Q1
CK Q1
D0 Q0
CK Q0